Volume of cylindrical, rectangular, and capsule tanks with partial-fill support.
Presets
Presets
Presets
Presets
Formulas and partial-fill math
Volume formulas per shape
Vertical cylinder: V = π × (d/2)² × h — diameter and height in the same unit give volume in that unit cubed.
Horizontal cylinder: same full-capacity formula V = π × (d/2)² × L where L is the barrel length.
Rectangular tank: V = L × W × H.
Capsule: V = π × (d/2)² × L + (4/3) × π × (d/2)³ — one cylinder plus two hemispheres (together forming a full sphere of diameter d).
Conversion to liters: 1 m³ = 1000 L; 1 US gallon = 3.785411784 L; 1 UK (imperial) gallon = 4.54609 L; 1 ft³ ≈ 28.3168 L.
Partial fill in a horizontal cylinder (circular segment)
When a horizontal cylinder is partially full, the liquid cross-section is a circular segment. With r = d/2 and fluid depth h from the bottom:
A = r² × arccos((r − h) / r) − (r − h) × √(2rh − h²)
Partial volume = A × L. The calculator above solves this automatically — the slider selects the depth h as a percentage of d.
Example: 36" diameter × 60" length horizontal cylinder, half full (h = 18"). A = 18² × arccos(0) − 0 = 324 × (π/2) ≈ 508.9 in². Volume ≈ 508.9 × 60 = 30 536 in³ ≈ 500.4 L ≈ 132.2 US gal (exactly half the full 264.4 US gal capacity).
FAQ
How many liters does a 55-gallon drum hold?
A standard US 55-gallon drum holds approximately 208.2 liters (55 × 3.7854). Nominal outside dimensions are 22.5" diameter × 33.5" height, but the usable inner volume is slightly less once you account for the chime and head thickness. Entering a 22" (55.9 cm) inner diameter × 33" (83.8 cm) inner height gives about 200 L, which is typical for real usable capacity.
What is the difference between US and UK (imperial) gallons?
They are not the same. 1 US gallon = 3.785 liters, while 1 UK (imperial) gallon = 4.546 liters — roughly 20% larger. A "1000-gallon" propane tank advertised in the US holds 3785 L; the same label in the UK would imply 4546 L. Always check which gallon your tank spec sheet uses, especially when comparing products across markets.
How do I measure tank volume when it is half full on its side?
For a horizontal cylinder, measure the fluid depth h from the bottom with a dipstick. Use the circular-segment formula in the details block above, or set the fill-level slider on the Horizontal cylinder tab to the percentage corresponding to h/d. For example, a 48" diameter tank with 12" of fluid is at h/d = 25%, which gives roughly 19.6% of full capacity — less than linear, because the cross-section is widest at the middle.
Why is my computed volume smaller than the tank's rated capacity?
Rated "nominal" capacity often refers to overall external dimensions, while the calculator uses inner dimensions to find actual liquid capacity. Wall thickness, dished heads, internal baffles, or a safety ullage (typically 10-20% air gap at the top for thermal expansion) all reduce working volume. For propane and LPG tanks, regulators fill only to about 80% to allow vapor space, so a 1000-gallon propane capsule legally holds about 800 gallons of liquid.
How accurate is the capsule formula for real LPG tanks?
The capsule formula assumes perfect hemispherical ends, which matches many small LPG, air, and propane tanks closely. Larger industrial vessels often use ellipsoidal (2:1 semi-elliptical) or torispherical (dished) heads, which hold slightly less than a true hemisphere. For rough planning the capsule formula is within 1-3% for most hemispherical-end tanks; for critical measurements use the manufacturer strapping chart.
Compute the liquid capacity of a tank from its inner dimensions. Pick a shape — vertical cylinder, horizontal cylinder, rectangular, or capsule — enter diameter/length/height in meters, centimeters, millimeters, feet, or inches, and the tool returns volume in liters, cubic meters, US gallons, UK gallons, and cubic feet at once. For a horizontal cylinder there is a fill-level slider that applies the circular-segment formula, so a half-submerged 36 in × 60 in cylinder returns about 500 L instead of the full 1000 L capacity. Worked examples: a 22 in × 33 in steel drum stores 208 L (55 US gal); a 1.2 × 1.0 × 1.16 m IBC tote holds 1000 L; a 41 in × 146 in propane capsule gives 3785 L nominal. Presets cover drums, totes, propane and fuel tanks, septic vessels, and air receivers.